Survey of Klebsiella pneumoniae producing extended-spectrum beta-lactamases: prevalence of TEM-3 and first identification of TEM-26 in France.

Crude extracts from 115 extended-spectrum beta-lactamase-producing Klebsiella pneumoniae isolates were analyzed biochemically. The TEM-3 type was encountered 108 times, SHV types were encountered 7 times, and the TEM-26 type was encountered only once. For the last one, the gene was identified; an adenine was detected at position 925, as in blaTEM-26B not in blaTEM-26.

Assessment of two penicillins plus beta-lactamase inhibitors versus cefotaxime in treatment of murine Klebsiella pneumoniae infections.

The in vivo efficacies of piperacillin, piperacillin plus tazobactam, ticarcillin, ticarcillin plus clavulanic acid, piperacillin plus clavulanic acid, and cefotaxime were compared in a mouse model of pneumonia induced by the SHV-1 beta-lactamase-producer Klebsiella pneumoniae. Each antibiotic was injected either once intraperitoneally at 24 h postinfection or at repeated times during 24 h. The efficacies of the drugs and therapeutic protocols were assessed by counting viable bacteria recovered from the lungs of mice sacrificed at selected times. No emergence of beta-lactam-resistant organisms was detected. Ticarcillin at 300 mg/kg was ineffective. Repeated injections of piperacillin at 300 mg/kg, either alone or in combination with tazobactam (8:1), led to a significant decrease in bacterial counts, but this was followed by bacterial regrowth. The pharmacokinetic analysis demonstrated that this short-lasting antibacterial effect was not due to a failure of piperacillin and/or tazobactam to penetrate the lungs. The combinations of ticarcillin at 300 mg/kg plus clavulanic acid (15:1) and piperacillin at 300 mg/kg plus tazobactam (4:1) were proven to be effective in that they decreased the bacterial burden in the lungs from 10(5) to < 10(3) CFU. This dose effect of tazobactam can be explained by its dose-dependent penetration in the lungs. Cefotaxime at 100 mg/kg and the combination of piperacillin (slightly hydrolyzed by SHV-1) at 300 mg/kg plus clavulanic acid (15:1) led to the best efficacy. Both of these treatments induced a decrease in bacterial counts of nearly 4 log10 units. The survival rates correlated with the quantitative measurements of in vivo bacterial killing. These experimental results obtained from the restricted animal model used here may help in the design of further protocols for clinical trials.

Assessment of a fluoroquinolone, three beta-lactams, two aminoglycosides, and a cycline in treatment of murine Yersinia pestis infection.

Amoxicillin, cefotaxime, ceftriaxone, gentamicin, doxycycline, and ofloxacin were active in vitro, like the reference drug streptomycin, against the virulent strain Yersinia pestis 6/69M. The comparative efficacies of these drugs in vivo were evaluated in a standardized and reproducible mouse model of systemic infection. Each antibiotic was injected intravenously once, at 24 h postinfection, and then repeatedly during 48 h. In vivo results were measured by counting the viable bacteria recovered from the whole spleens of mice sacrificed at selected times. All the drugs were manifestly successful; ceftriaxone, ofloxacine, and the reference drug were the most effective. Therefore, gentamicin and doxycycline could be used, depending on the clinical forms of the Y. pestis infection. Further investigations on beta-lactams, especially those used in the present study, could be carried out to confirm or not confirm their activities against Y. pestis. Ofloxacin appeared to be as active and to perform as rapidly as streptomycin in the treatment of murine Y. pestis infection, which is in agreement with the previous successes obtained with the use of fluoroquinolones in the treatment of murine infections caused by other pathogenic yersiniae.

Antibiotic treatment of Yersinia enterocolitica septicemia: a retrospective review of 43 cases.

Of 53 documented cases of Yersinia enterocolitica septicemia reported to the French national registry between 1985 and 1991, 43 files contained sufficient information on antibiotic treatment to be analyzed retrospectively. All patients had at least two positive cultures of blood collected before the initiation of treatment. All strains were susceptible in vitro to the antibiotics that are usually active against gram-negative rods except for older beta-lactam agents (i.e., aminopenicillins and first-generation cephalosporins). No multiresistant strain was isolated. Only four (7.5%) of the 53 patients died. Aminopenicillins, first-generation cephalosporins, and--when prescribed alone--amoxicillin/clavulanate were not effective. Third-generation cephalosporins, most often used in combination with other antibiotics, were successful in 85% of cases. Fluoroquinolones--alone or in combination--cured all of 15 infections, with patients improving rapidly and becoming apyretic within 1-4 days. These agents therefore seem to constitute the best treatment.

Failure of beta-lactam antibiotics and marked efficacy of fluoroquinolones in treatment of murine Yersinia pseudotuberculosis infection.

The treatment of yersiniosis by beta-lactams is questionable considering the proven failure of newer beta-lactams for treating murine Yersinia enterocolitica infection. Another modality of experimental treatment was performed with a virulent strain of Y. pseudotuberculosis (nonproducer of beta-lactamase) highly susceptible (in terms of MICs) to amoxicillin, cefotaxime, ceftriaxone, imipenem, doxycycline, gentamicin, and ofloxacin. The in vivo comparative efficacy of these drugs was evaluated in a standardized and reproducible mouse model of systemic infection. Each single antibiotic was injected intravenously once, at 30 h after intravenous inoculation of the infective strain, and then repeatedly (at 30, 52, and 76 h postinfection). In vivo results were measured by counting the viable bacteria recovered from the whole spleens of mice sacrificed at selected times. Cefotaxime, even at high doses (250 mg/kg of body weight), was totally ineffective. Amoxicillin and imipenem at high doses (200 and 100 mg/kg, respectively) and ceftriaxone at usual doses (20 mg/kg) were active only in stopping bacterial proliferation to a more or less slight degree. Ceftriaxone was able to reduce viable counts in the spleen only at high doses (200 mg/kg), as were gentamicin (20 mg/kg) and doxycycline (125 mg/kg). Ofloxacin at the low dose of 5 mg/kg was demonstrated to be very effective by the very significant decrease observed in bacterial numbers from 10(6) to 10(3) CFU per spleen. The pharmacological parameters do not in themselves explain all the discrepancies between the in vitro and in vivo activities of beta-lactams on yersiniae. No emergence of beta-lactam-resistant organisms, which could explain the failure of beta-lactams, was detected. Thus, their use should be delayed in the therapy of human yersinosis until further investigations are carried out. The fluoroquinolone appeared more active and rapid than reference drugs in the treatment of murine yersinosis, which confirms initial clinical results.

Evidence for broken minocycline by NMR and HPLC techniques: a new additional resistance mechanism mediated by tetB determinant.

As demonstrated by microbiological assays, a decrease in the active minocycline level occurs in spent media from each Escherichia coli K12 recipient containing one of 10 different plasmids bearing tetB determinants. No such decrease was detected when tetA, C, D or E determinants were tested under the same conditions. Likewise, no decrease in tetracycline or doxycycline levels was detected when 20 plasmids bearing tetA to E determinants were tested. Studies carried out by nuclear magnetic resonance and high pressure liquid chromatography proved that minocycline is broken by a mechanism mediated by the tetB determinant. This new mechanism can be considered as additional to the active efflux of minocycline.

Failure of newer beta-lactam antibiotics for murine Yersinia enterocolitica infection.

Cefotaxime, imipenem, gentamicin, and doxycycline were active in vitro against the virulent serotype O8 Yersinia enterocolitica WA strain. Amoxycillin was inactive. The in vivo activity of these drugs was evaluated in a standardized and reproducible mouse model of systemic infection. Each single antibiotic was injected intravenously 30 h after intravenous inoculation of Y. enterocolitica WA. In vivo efficacy was measured by counting the viable bacteria recovered from the whole spleens of mice sacrificed at selected times. Doxycycline and gentamicin were active in stopping bacterial proliferation. Cefotaxime and imipenem, even at high doses (250 and 100 mg/kg of body weight, respectively), were totally ineffective, as was amoxycillin. Bacterial inocula (10(7)), recovered from either the in vitro growth or the infected spleens, were plated on cefotaxime or imipenem concentration gradients in agar; no emergence of beta-lactam-resistant organisms was detected. Based on these experiments it is not possible to explain, from any given property of the antibiotic, the bacteria, or the host, the discrepancy between the in vivo and in vitro activities of cefotaxime and imipenem. On the basis of these results, the use of newer beta-lactam antibiotics should be delayed in the therapy of human Y. enterocolitica infections until further investigations are carried out.

In vitro susceptibilities of 126 clinical isolates of Yersinia enterocolitica to 21 beta-lactam antibiotics.

The MICs of 21 beta-lactam antibiotics were measured against 126 clinically significant and epidemiologically unrelated Yersinia enterocolitica isolates. The most active antimicrobial agents tested (geometric means of MICs) were ceftriaxone, cefotaxime, ceftizoxime, and cefmenoxime (0.06 to 0.08 micrograms/ml). Mezlocillin (1.36 micrograms/ml) and piperacillin (1.57 micrograms/ml) were the most active penicillins. Aztreonam and imipenem had MICs of 0.44 and 0.24 micrograms/ml. All isolates exhibited some degree of resistance against ampicillin (MICs, greater than or equal to 4 micrograms/ml) and cephalothin (MICs, greater than or equal to 8 micrograms/ml). Cephalosporinase or penicillinase activities were expressed by all isolates. A principal component analysis of MIC data separated the major serotypes (O3, O9, O8, and O5,27). The MCBs of 14 newer beta-lactams were measured against 10 clinical isolates. On the basis of the ratio of MBC to MIC (expressed in dilution factors), a real bactericidal activity was only observed for imipenem (MBC/MIC = 1). For the other newer beta-lactams, the ratios ranged from 4 to 8.

Chelocardin-inducible resistance in Escherichia coli bearing R plasmids.

Two plasmid-linked tetracycline resistance characters, tet A and tet B, were distinguishable in part, according to the level of resistance they conferred to minocycline (<3 mug/ml for tet A; >6 mug/ml for tet B). Escherichia coli K-12 strains that harbored the tet B character were also resistant to tetracycline but susceptible to chelocardin. In such tet B strains, subinhibitory concentrations of tetracycline could induce resistance to chelocardin as well as to otherwise inhibitory concentrations of tetracyclines. Chelocardin itself was ineffective as an inducer and therefore could be used to select constitutively resistant mutants. E. coli K-12 strains harboring the tet A character were also resistant to tetracycline and susceptible to chelocardin; tetracycline did not induce resistance to chelocardin in these strains.

Incompatibility groups and the classification of fi - resistance factors.

Incompatibility between R factors has been reported by several authors, and four incompatibility groups have already been described by Datta and Hedges among Rfi(-) factors. The stability of 12 plasmids in pairs was studied after 116 crosses, and five new groups were found, designated 5, 6, 7, 8, and 9. Each plasmid studied belongs to one single group. Incompatibility between plasmids in pairs is a clear-cut phenomenon, is easy to observe, and can provide a reliable method for recognizing and classifying resistance factors, and for tracing their spread among bacterial species.